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Apr 1968

Volume 39, Issue 4, pp. 441-622

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Mass‐Energy Spectrometer for Space Plasmas

K. W. Ogilvie, N. McIlwraith, and T. D. Wilkerson

Rev. Sci. Instrum. 39, 441 (1968); http://dx.doi.org/10.1063/1.1683404 (11 pages) | Cited 21 times

Online Publication Date: 10 November 2003

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A satellite‐borne instrument for the study of the interplanetary medium is described in detail. This plasma experiment illustrates a whole class of such measurements that can now be done on small unmanned scientific satellites. Plasma ions are resolved in both energy and mass per unit charge in order to determine hydrogen‐helium abundance ratio, ion temperatures in the ``solar wind'' and transition region, and the angular distributions and fluctuations of ion flux. Protons and alpha particles with energy per unit charge between 300 and 5000 eV are resolved to better than 5 in 103 and their energy spectrum determined. Instead of current measurements, we employ single ion counting with an efficiency of 75% at rates up to 3×107 sec−1. A histogram of counts against angular rotation is formed with a quantization of 23° and its area, variance and the azimuthal position of the peak derived by a small computer for transmission to the earth over a data link with a capacity of approximately 6 bits sec−1. Provision is made for a preliminary study of variations in the ion flux with periods greater than a few seconds. Two companion papers present the details of developments which proved necessary for this experiment and are of wider interest as well.

On‐Board Plasma Data Processor

David H. Schaefer and James W. Snively

Rev. Sci. Instrum. 39, 452 (1968); http://dx.doi.org/10.1063/1.1683406 (7 pages)

Online Publication Date: 10 November 2003

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A computing device that calculates quantities related to the mean, variance, and mode of the distribution of plasma as a function of the azimuthal angle of the spin stabilized satellite is aboard Explorer XXXIV. The device uses a combination of integrated circuits and discrete components including tunnel diodes. Performing computations aboard the spacecraft and telemetering the results of the calculations permits important features of the data to be sent using about one‐twentieth of the number of information bits that would be required to transmit histograms of the collected data.

Crossed Field Velocity Selector

K. W. Ogilvie, R. I. Kittredge, and T. D. Wilkerson

Rev. Sci. Instrum. 39, 459 (1968); http://dx.doi.org/10.1063/1.1683407 (7 pages) | Cited 10 times

Online Publication Date: 10 November 2003

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The paths of particles passing through crossed fields are calculated, with special application to the case where the particle does not complete a cycloidal oscillation. The use of such crossed fields in velocity selectors for space flight and in the laboratory is discussed. Curves are given which help in the choice of parameters for such applications.

Tunnel Diode‐Transistor Binary Scaler

Z. C. Tan and P. C. Maxwell

Rev. Sci. Instrum. 39, 466 (1968); http://dx.doi.org/10.1063/1.1683408 (3 pages)

Online Publication Date: 10 November 2003

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This paper describes a new type of tunnel diode‐transistor binary scaler which is very simple in concept and in design. It is capable of operating reliably at input pulse repetition rates in excess of 200 MHz. A significant feature of the scaler is that there is no maximum input pulse width restriction. Input and output circuits which allow the scaler to operate over a wide range of input driving conditions and to be cascaded directly with similar scalers are also presented.

Precision Mask Changer for Ultrahigh Vacuum Systems

J. A. Seitchik, B. F. Stein, and N. Goldberg

Rev. Sci. Instrum. 39, 469 (1968); http://dx.doi.org/10.1063/1.1683409 (3 pages)

Online Publication Date: 10 November 2003

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A precision mask changer has been fabricated which uses a novel alignment technique to obtain precise registration between successive evaporations onto heated substrates in ultrahigh vacuum. A basic feature is the manipulation of the substrate while it is under vacuum and at the desired temperature. The registration process is observed by means of a split field microscope with objectives which can be individually focused on two areas of the substrate. Patterns have been registered to better than 5μ with the substrate at temperatures up to 200°C. In all cases the chamber pressure was 2×10−10 Torr.

NQR Spectrometer Using Field Effect Transistors

T. Lakshmi Viswanathan, T. R. Viswanathan, and K. V. Sane

Rev. Sci. Instrum. 39, 472 (1968); http://dx.doi.org/10.1063/1.1683410 (4 pages) | Cited 8 times

Online Publication Date: 10 November 2003

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The advantages of using field‐effect transistors (FET) for NQR spectrometer design are discussed. An experimental method of evaluating the performance of different oscillator configurations and optimizing the circuit parameters for best sensitivity is outlined. An NQR spectrometer system is described.

Continuous Averaging of X‐Ray Diffraction Data Using a Multichannel Analyzer

John W. Weymouth, James Costello, Sanford Schuster, and Paul Schulze

Rev. Sci. Instrum. 39, 476 (1968); http://dx.doi.org/10.1063/1.1683411 (2 pages) | Cited 5 times

Online Publication Date: 10 November 2003

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A continuously averaging system is described in which a multichannel analyzer is coupled to an x‐ray diffractometer. The motion of the arm of the diffractometer is synchronized with the channel advance so that there is a 1 to 1 correspondence between 2θ increments and channels. With this system a weak x‐ray diffraction signal may be scanned repeatedly and the signal built up against the random noise introduced by fluctuations in the generating and detecting system with periods long compared to the channel dwell time. Other convenient uses of the analyzer in handling the x‐ray diffraction data are briefly mentioned.

Fitting Experimental Data Using the Method of Least Squares

S. Margulies

Rev. Sci. Instrum. 39, 478 (1968); http://dx.doi.org/10.1063/1.1683412 (3 pages) | Cited 9 times

Online Publication Date: 10 November 2003

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With a view toward facilitating proper use of computer curve‐fitting programs, the method of least squares for fitting smooth curves to experimental data is discussed. The distinction between the problem when the functional form of the data is known, and when it is not known, is emphasized. For the latter case, the usual procedure of using an expansion having M linear coefficients to represent the functional form is considered. In making such a fit, care must be exercised in choosing M. Although the least‐squares sum decreases as M is increased (tending to zero as M approaches N, the number of data points), the resulting fit is not necessarily a better representation of the data. It is shown that, in the extreme case where M=N, the least‐squares fit is identical to a linear expansion which is constrained to pass through every point, and such a fit is, of course, meaningless. Tests for the statistical significance of fits are discussed.

Four‐Electrode Null Techniques for Impedance Measurement with High Resolution

Herman P. Schwan and Clifford D. Ferris

Rev. Sci. Instrum. 39, 481 (1968); http://dx.doi.org/10.1063/1.1683413 (5 pages) | Cited 69 times

Online Publication Date: 10 November 2003

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At low frequencies, the normally difficult measurement of the dielectric properties of conducting materials is severely compromised by electrode polarization. This problem at the electrode‐sample interface arises from the modulation of the normal dc boundary potential by the passage of alternating current. A solution, permitting a conductance resolution of 1:105 for frequencies between 10 cps and 1 kc, is to use a second noncurrent‐carrying pair of electrodes to measure the voltage across the sample and to employ a null technique for obtaining the required precision. Several four‐electrode null techniques are proposed, each having certain relative merits. In all cases the resolution in capacitance is shown to be governed by a combination of the resolution in conductance, the sample properties, and the frequency of the measurement.

High Speed Optical Stopped‐Flow Apparatus

R. L. Berger, B. Balko, W. Borcherdt, and W. Friauf

Rev. Sci. Instrum. 39, 486 (1968); http://dx.doi.org/10.1063/1.1683414 (8 pages) | Cited 16 times

Online Publication Date: 10 November 2003

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A stopped flow apparatus for the study of fast reactions in solution is described. The measured dead time was 270 μsec with an uncertainty in the measurement of 50 μsec. At 410 mμ and an optical density of about 0.09 a change of 0.0044 optical density units could be observed at a flow velocity of 30 m∕sec through a 3.0 mm observation tube. Ten milliliters of each of the two reagents are required to fill the system, and less than 1.0 ml of each needs to be expended per experiment.

High Resolution Mixer for the Study of the Kinetics of Rapid Reactions in Solution

Robert L. Berger, Bohdan Balko, and Howard F. Chapman

Rev. Sci. Instrum. 39, 493 (1968); http://dx.doi.org/10.1063/1.1683415 (6 pages) | Cited 26 times

Online Publication Date: 10 November 2003

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The turbulent wake of a spherical surface was utilized as part of a mixer for fast reaction studies. The mixer is capable of mixing two solutions within 100 μsec at a flow velocity of 30 m∕sec. Optical and thermal methods were used to study the mixer. Highly efficient mixing was achieved for 120 cP solutions as well as aqueous solutions.

Measurement and Computation of Thermojunction Response Times in the Submillisecond Range

Bohdan Balko and Robert L. Berger

Rev. Sci. Instrum. 39, 498 (1968); http://dx.doi.org/10.1063/1.1683416 (6 pages) | Cited 5 times

Online Publication Date: 10 November 2003

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A simple method is presented for measuring the response of thermocouples in liquid media. Response times down to 50 μsec have been measured. Various coating techniques for obtaining fast responding electrically insulated junctions are discussed. The effect of thermocouple materials and insulation coatings on the response time has been experimentally determined and the results compared with a computer calculation simulating the physical system. The computer calculation involves two difference equations and solves a multilayered media problem without the introduction of heat transfer coefficients. The results agree to within experimental error.

Multichannel Photoionization Chamber

H. H. Kim, Shardanand, A. J. Caruso, and A. E. Barrington

Rev. Sci. Instrum. 39, 503 (1968); http://dx.doi.org/10.1063/1.1683417 (3 pages) | Cited 2 times

Online Publication Date: 10 November 2003

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A novel multichannel photoionization chamber has been devised for use in the vacuum ultraviolet to measure absorption, photoionization yield and photoionization coefficients of gases, and consequently, the absolute intensity of light sources. The theory, design, and operational advantages of the device are discussed. In particular, it is shown that for each channel the ion‐current‐pressure plot passes through a maximum; and the value of the pressure at the ion current maximum is the only experimental measurement necessary to determine the absorption coefficient of the filling gas.

Magneto‐Optic Measurement by Sample Exchange

S. Broersma and P. E. Hendrickson

Rev. Sci. Instrum. 39, 506 (1968); http://dx.doi.org/10.1063/1.1683418 (3 pages)

Online Publication Date: 10 November 2003

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For a precise determination of small differences in magneto‐optic rotation an exchange method has great advantages. In this, the magnetic field is effectively kept constant, but it need not be known to high accuracy. Equality of temperature and optical bandwidth is ensured by the method. A cart, supporting two sample tubes, is shuttled back and forth along the light beam such that in each extreme position a different sample is magnetized. With a 15 min measurement, an accuracy of 2×10−4 has been obtained. The optical stability by itself is 3×10−5.

High Intensity Light Source

J. D. Harper

Rev. Sci. Instrum. 39, 509 (1968); http://dx.doi.org/10.1063/1.1683419 (2 pages)

Online Publication Date: 10 November 2003

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A high intensity argon flash which utilizes high explosive is described. The flash is simple to construct and offers special advantages when the interior of partially closed objects must be illuminated for photography.

Whole‐Body NMR Spectrometer

Jasper A. Jackson and Wright H. Langham

Rev. Sci. Instrum. 39, 510 (1968); http://dx.doi.org/10.1063/1.1683420 (4 pages) | Cited 10 times

Online Publication Date: 10 November 2003

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A low‐frequency NMR spectrometer has been built that will accommodate sample volumes of 0.2 and 1.25 liters. A shielded solenoid provides a uniform field of about 10 G. Signals are detected by a symmetrical rf bridge whose coils are bank wound of litz wire with Q∼300 to 400 at 40 kHz. In the smaller coil the homogeneity is sufficient to distinguish signals of protons in protein from those in fat and water. Spectra have been obtained from gelatin, whole eggs, egg whites, egg yolks, and dead mice. In addition, what is believed to be the first NMR signal ever obtained from a whole living animal has been taken on an anesthetized rat.

Technique for Accurate Measurement of the Electrical Conductivity of Shocked Fluids

A. C. Mitchell and R. N. Keeler

Rev. Sci. Instrum. 39, 513 (1968); http://dx.doi.org/10.1063/1.1683421 (10 pages) | Cited 21 times

Online Publication Date: 10 November 2003

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A method of accurately measuring the electrical conductivity of shock compressed fluids is described. It is shown that when optimum geometry is used and when the shock impedance of fluid and electrodes are properly taken into account, the effect of reflected shocks can be understood. Data for carbon tetrachloride over a pressure range of 65 to 160 kilobars and a conductivity range of 10−1 to 10−7 mho∕cm are presented. The accuracy of the measurements is better than 10%.

Simple NMR Probe for Use in Superconducting Solenoids

R. J. Higgins and Yung Kwang Chang

Rev. Sci. Instrum. 39, 522 (1968); http://dx.doi.org/10.1063/1.1683422 (2 pages) | Cited 10 times

Online Publication Date: 10 November 2003

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A simple nuclear magnetic resonance probe, for field calibration use over the 10–50 kG magnetic field range in superconducting solenoids at liquid helium temperature, is described. The probe uses the 27Al resonance from aluminum powder, and is attached without electronic modification to a commercial NMR (marginal oscillator) gaussmeter.

Remote Control Viscometer

E. L. Cussler and Raymond M. Fuoss

Rev. Sci. Instrum. 39, 524 (1968); http://dx.doi.org/10.1063/1.1683423 (5 pages) | Cited 1 time

Online Publication Date: 10 November 2003

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A remote control viscometer, designed for use in a high pressure bomb up to 5000 atm, is described. Operation is as follows: a solenoid lifts a tapered piston, which then drops into a cylinder. On the down stroke, needles attached rigidly to the piston dip successively into two mercury wells, the first one starting an electric timer and the second stopping it. Three insulated leads into the bomb are required; the case acts as the common ground. Relative viscosities can be reliably measured within 2%. Results at 30° are given over the pressure range for n‐propyl ether, cumene, n‐butyl chloride, and 1,2‐dichloroethane.

Photopeak Efficiency of a Well‐Type Scintillation Detector

W. G. Hanson and B. W. Sargent

Rev. Sci. Instrum. 39, 529 (1968); http://dx.doi.org/10.1063/1.1683424 (3 pages)

Online Publication Date: 10 November 2003

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The detection and photopeak efficiences of a NaI cylindrical crystal, 7.62 cm diam and 7.62 cm high, containing a 0.63 cm diam well, 4.13 cm deep, were experimentally determined for 0.51 MeV gamma radiation from 11C positron annihilation. The pulse‐height distribution measured with the source on top of the crystal was used with probability theory to obtain an approximate synthetic summed spectrum for the source in the well. This in turn was used to analyze the observed pulse‐height distribution for the source in the well. The detection and photopeak efficiencies are 0.70±0.02 and 0.49±0.01, respectively, from which the photofraction is 0.70±0.03. Agreement with calculated values is good.

Instrument for Microradiography of Small Specimens

Robert S. Ledley and Helen C. Sing

Rev. Sci. Instrum. 39, 531 (1968); http://dx.doi.org/10.1063/1.1683425 (3 pages)

Online Publication Date: 10 November 2003

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An instrument originally designed for contact microradiography of very thin rat bone sections is described. It is not limited to use for bone, but may be used for any biological or mineral specimens small enough for the specimen opening (0.63 cm diam). The recording material is 35 mm spectroscopic film and up to five specimens may be imaged on a single film frame.

Cylindrical Capacitor as an Analyzer. II. Relativistic Part

H. Z. Sar‐El

Rev. Sci. Instrum. 39, 533 (1968); http://dx.doi.org/10.1063/1.1683426 (8 pages) | Cited 9 times

Online Publication Date: 10 November 2003

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The study of the dynamic and optical properties of the cylindrical capacitor as an analyzer for charged particles is extended to the relativistic region. The proposed analyzer is found to be absolutely unrestricted by the relativistic effect, the latter introducing some changes which do not however impair the analytical features of the device. The emission angle for which there is a second order focus is energy‐dependent, shifting from θ0=42°18.5′ in the nonrelativistic case to θ0=55° in the ultrarelativistic case. It is shown that the usual derivation of the relativistic formulae from the nonrelativistic ones by replacing the nonrelativistic potential difference by an ``effective relativistic potential difference'' is incorrect for electrostatic devices, unless this quantity is given a specifically ``electrostatic'' form, distinct from the magnetic one. The figures of merit of the analyzer concerning resolution and luminosity are comparable with those of the best magnetic spectrometers. The analyzer seems to be simpler and cheaper than the magnetic type, but calls for very high deflecting voltages, which may be a disadvantage in operation.

Absolute Efficiency Measurements of NE‐213 Organic Phosphors for Detecting 14.5‐ and 2.7‐MeV Neutrons

T. A. Love, R. T. Santoro, R. W. Peelle, and N. W. Hill

Rev. Sci. Instrum. 39, 541 (1968); http://dx.doi.org/10.1063/1.1683428 (7 pages) | Cited 3 times

Online Publication Date: 10 November 2003

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The absolute efficiency of two NE‐213 organic phosphors for detecting 14.5‐ and 2.7‐MeV neutrons has been determined by the associated particle technique with the recoil particles from the T(d,n)4He and D(d,n)3He reactions. The output of the neutron detector was placed in coincidence with the helium recoil pulses and the efficiency of the detector was obtained as the ratio of the coincidence counts to the helium recoil counts. The scintillators were 12 cm in diameter and had thicknesses of 2.61 and 6.10 cm, and each was preceded by a 5‐mm thick NE‐102 plastic scintillator and followed by a 3.3‐cm (average thickness) Lucite light pipe. The detection efficiency, for neutrons striking the central 25% of the detector area, was measured as a function of the bias level on a tunnel diode driven by the current pulse from dynode 14 of a 58AVP multiplier phototube and also as a function of a bias threshold on the total light output. The bias level was calibrated in terms of the pulse‐height spectra resulting from the interactions in the phosphors of gamma rays of several energies. Comparisons were made between experimental efficiencies and those obtained from Monte Carlo calculations. For a threshold of 40°±5 keV electron total light equivalent, the agreement is within 7% for the smaller detector and 1.5% for the larger.

Device for Producing Very Low Magnetic Fields

Robert E. Brown

Rev. Sci. Instrum. 39, 547 (1968); http://dx.doi.org/10.1063/1.1683429 (4 pages) | Cited 2 times

Online Publication Date: 10 November 2003

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A volume containing a reduced magnetic field may be obtained inside a lead foil sack by opening the folded sack at 4.2°K when the lead is superconducting. A multi‐stage magnetic flux ``vacuum pump'' based upon this idea was used to reduce earth's field to below 10−6 Oe in a volume of several hundred cubic centimeters. The superconducting sack shields this volume against the magnetic field fluctuations of the laboratory environment. The estimated noise amplitude in the low field space is 10−8 Oe. A glass Dewar inserted into the sack permits working in the low field space at controlled temperatures near room temperature. The system has had extensive use for the study of the long term stability of flux‐gate magnetometer sensors.

Noise in Hot‐Wire Anemometers

Peter Freymuth

Rev. Sci. Instrum. 39, 550 (1968); http://dx.doi.org/10.1063/1.1683430 (8 pages) | Cited 15 times

Online Publication Date: 10 November 2003

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An analysis is given of the electronic noise and the signal‐to‐noise ratio for constant‐temperature and constant‐current hot‐wire anemometers. The analysis shows that both anemometers are equivalent in their signal‐to‐noise ratio if the noise sources are equivalent and the hot‐wires are operated at the same conditions. A discussion of the theoretical results and a comparison of both anemometer types based on these results are given. In addition, some noise measurements on a constant‐temperature anemometer and the methods to obtain them are reported and compared with theoretical results. The agreement between measured and theoretical results is rather good.
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